The Bridge got off to a corker, surely now it ranks as one of the best crime shows on TV?

What makes a great TV detective? Every so often, a list is compiled of the greatest small-screen sleuths of all time and the usual suspects crop up: Hercule Poirot, Cagney & Lacey and so on. But, for my money, they’re all beaten into a cocked hat by Saga Norén, sociopathic scion of the Swedish police.

Yes, The Bridge (BBC4) is back, complete with TV’s best ever theme tune – there’s another list you can have fun debating – and Norén, played to perfection by Sofia Helin (right with Kim Bodnia), is doing her best to pretend to be part of the human race. She’s even moved in with a bloke called Jakob, not that she’s the ideal girlfriend.

‘What does he do?’ inquired cop partner Martin, a typical sort of question. ‘I don’t know,’ says Saga. ‘Should I?’ The Bridge is shot through with such bleakly comic exchanges, it’s what lifts this Danish-Swedish cop show above the competition. It’s the fabric on which the plot is stitched but it never overwhelms the action.

We’ve moved on since we were last perched precariously on the serpentine Øresund, the link between Copenhagen and Malmö. Martin is still reeling from the death of his son and, in a contrary twist, it’s a reunion with Saga that drags him back to the real world, her very lack of empathy just the jolt he needs. She treats him just the way she used to.

And their new case is a corker, a tale of eco terrorists in animal masks in the habit of making videos with placards reading ‘The World Is Bigger Than Us’ and floating the idea that we could all be infected with the plague if the wrong crackpots got hold of the right poison. The combination of threat and human relationships is what The Bridge gets so right.